Apparatus for use on floating drilling platforms



Dec. 29, 1964 J. A. REED u I 3,163,005 APPARATUS FOR USE ON FLOATING DRILLING PLATFORMS Filed Nov. 19, 1962 2 Sheets-Sheet 1 CROWN BLOCK 0 I5 ,-ii' m FIG- I. I2

DEAD LINE BLOCK '4 36 COMPENSAT'NG CYL. I 35 1 I TO CONTROL UNIT SWIVEL l8 LIVE LINE 28 l0 FLOATING PLATFORM WEIGHT INDICATOR RESERVOIR & CONTIgfiJL UNIT iii INVENTOR. JOHN A. REE D, II.

DRILL an ATTORNEY.

J. A. REED u APPARATUS FOR USE ON FLOATING DRILLING PLATFORMS Filed NOV. 19, 1962 2 Sheets-sheaf. 2

. w cw k E N N R E E 8 w G G O O 6 R I R 4 T T 6 N N m W H A E L I M 0 m m m R A N U 0 N C A m a M 3 w; 7 I 7 ll 9 2 R 9 7 6 m A L U l U K 3 c C C O B A L B PILOT CONTROL TH ROTTLING VALVE FIG RESERVOIR INVENTOR.

{JOHN A. REEDJI.

TO SWIVEL A T TOR NEY United States Patent 3,163,065 APPARATUS 1 9R USE ON FLQATlNG DRILLING PLATFORMS John A. Reed 11, Los Alamitos, Calih, assignor, by mesne assignments, to Jersey Production Research Company,

Tulsa, Okla, a corporation of Delaware Filed Nov. 1?, 1962, Ser. No. 238,445 1 Claim. (Cl. 60-51) This invention concerns apparatus for maintaining substantially constant tension on drill pipe and the like suspended from a floating offshore structure.

When a well or borehole is drilled into submerged land from a floating oflshore drilling platform, substantially constant weight must be maintained on the drill bit to keep it feeding properly into the earth formations notwithstanding vertical oscillations of the drilling platform caused by Wave action.

Various systems and techniques have been proposed to achieve constant bit weight when drilling under these conditions and it is a primary object of the present invention to provide bit weight control apparatus which not only generally improves the performance and operation of these previous arrangements; but, in addition, functions to permit varying of the absolute value of bit weight to be maintained as drilling of the borehole progresses, as well as control of the sensitivity of the weight control system as the total load on the system changes.

Briefly, the invention comprises a cylinder and piston movably arranged in the cylinder from which a drill string and drill bit are suspended; and means including a pressure balanced accumulator, a constant pressure variable volume pump, and a pressure controlled throttling valve for supplying constant pressure, variable volume hydraulic energy to the piston in order to automatically maintain drill bit weight control.

The above object and other objects and advantages of the invention will be apparent from a more detailed descniption thereof when taken with the drawings wherein:

FIG. 1 is a vertical view of a drilling platform floating on a body of water with the apparatus of the invention for controlling bit weight mounted on the platform and connected to the drilling equipment; and

FIG. 2 is a diagrammatic view showing the bit weight control apparatus of FIG. 1 in greater detail.

For a complete description of the invention further reference is made to the drawings wherein in FIG. 1 is shown an offshore drilling platform or barge 10 anchored and floating in a body of water 11 and on which is arranged conventional drilling equipment including derrick structure 12, live line 13, dead line 14, crown block 15, traveling block 16, circulating fluid conduit 13, swivel 19, rotary 2t) and draw-works 21. A borehole 25 is being drilled in the earth underlying the body of Water 11 by means of drill bit 26 carried on the end of a string of drill pipe 27, which is connected to a Kelly joint 28, which in turn is connected to swivel 19. One part of the equipment for maintaining substantially constant weight on drill bit 26 to compensate for vertical movement of platform 10, viz., the piston and rod designated 30, is interposed between block 16 and swivel 19. The remainder of the control or compensating apparatus designated 31 is mounted on floating platform 10.

Details of the compensating apparatus 36-31 are shown in FIG. 2. Part 30 of this apparatus includes an elongated cylinder 35 suspended from traveling block 16 by links 36. Cylinder 35 is provided with openings 37 in its upper end and an opening 38 in its lower end. The latter opening has connected to it a conduit 39. A piston 40, which divides the interior of cylinder 35 into upper and lower chambers 41 and 42 respectively, is slidably 3,163,665 Patented Dec. 29, 1964 ice arranged in cylinder 35. A rod 43, from which drill pipe string 27 and drill bit 26 are suspended through swivel 19, extends through the lower end of cylinder 35 and is attached to piston 40. A seal 44, arranged in the lower end 5 of cylinder 35, closes off the space surrounding rod 43 in the opening in cylinder 35 through which rod 43 extends in order to prevent leakage of liquid from chamber 42.

The remainder of the compensating apparatus 31 includes a reservoir of liquid 46, e.g., oil or water; a constant speed variable volume pump 47, e.g., a centrifugal pump, driven by a motor 48; an accumulator 49 in which is arranged a floating or free piston 56 dividing the interior of accumulator 49 into an upper gas-containing chamber 51 and a lower liquid, e.g., oil or water, containing chamber 52; and a pressure controlled throttling valve 53.

Conduit 39 serves as an inlet and outlet for supplying liquid to and discharging liquid from chamber 42 as cylinder 35 rises and falls in response to movements of drilling platform 10. Reservoir 46 supplies oil to conduit 39 through pump 47 and conduit 54 in which is positioned a check valve 55.

An inlet-outlet conduit 56 for carrying liquid into and from chamber 52 of accumulator 49 also connects into conduit 39. A manually operable valve 57 is positioned in conduit 56. A conduit 58 for discharging liquid into ,reservoir 46 from chamber 42 and chamber 52 also is connected to conduit 39. Valve 53 is positioned in conduit 58, and adjacent valve 53 a conduit 59 is connected into conduit 58 to supply fluid pressure to the pilot control arrangement generally designated 60 used to control the operation of valve 53. The pilot control arrangement 60 and valve 53 are commercially available, conventional equipment and may be of the type disclosed in the Composite Catalog of Oil Field Equipment and Services, 1960-61, 24th Edition. Pilot arrangement 60 is a Fisher Governor Company Type 4100-U, or equal, control pilot shown on page 1840. Throttling valve 53 is a Fisher Type 657A, or equal, diaphragm control valve with the inner valve reversed to provide a reverse acting back pressure regulator arrangement. The direct acting arrangement is shown on page 1838. Valve 53 is operated by a spring biased diaphragm 61, the position of which is controlled by fluid pressure in conduit 62. Increased pressure in conduit 62 opens valve 53 to permit flow of oil into reservoir 46 through conduit 58.

The fluid pressure in conduit 62 is controlled by a vent flapper in housing 63, which permits more or less pressure to pass into conduit 62 from a source of control air 64, through a regulator 65 and conduit 66. The position of the vent flapper in housing 63 is controlled by the bourdon tube 67, which in turn is contracted and expanded by pressure of the liquid in conduit 59.

Upper chamber 51 of accumulator 49 is supplied with high pressure gas from a gas source 68, e.g., nitrogen bottles, through a conduit 69 in which is positioned a regulator 71 a check valve 71, and a manually controlled valve 72. A manual valve 73 also connects to upper chamber 51 to reduce pressure in chamber 51 whenever it is suitable to do so, such as prior to starting a new borehole. Pressure gauges 74 are positioned on the apparatus at various points as desired.

The pressure of the oil in chamber 42 determines the force or weight on drill bit 26. The higher the pressure in chamber 42, the less will be the weight on the drill bit; and accordingly, the lesser the pressure in chamber 42, the greater will be the weight on the drill bit. Therefore, by controlling the liquid pressure in chamber 42, the net weight of the string of drill pipe 27 placed on drill bit 26 can be regulated; and to maintain the net weight on drill bit 26 substantially constant, the pressure of the oil in chamber 42 must be maintained substantially constant.

In order to maintain the liquid pressure in chamber 42 constant, the pressure fluctuations in chamber 42 caused by vertical movement of cylinder 35 resulting from vertical movement of platform 19 must be compensated for by the pressure system described supra. Accumulator 49 provides a rapid response to pressure transients caused by vertical motion of drilling platform whereas, reservoir 46 and its assocaited equipment, pump 47 and throttling valve 53, provide for system volume changes associated with increased depth of borehole 25 as drilling progresses and large movements of drilling platform It).

Operation As an example of the operation, pump 47 is running maintaining a constant pressure in chamber 42 and chamber 52 equal to the pressure in chamber 51. The volume pumped by pump 47 to maintain said pressure is con tinually released through throttling valve 53. When wave action causes drilling platform 10 to rise, cylinder 35 also is carried upwardly relative to piston 40; and downward movement of platform 10 causes cylinder 35 to move downwardly relative to piston 4!). When cylinder 35 rises relative to piston 40, pressure of the liquid in chamber 42 increases. To maintain piston 46* at a relatively constant level, liquid in chamber 42 discharges through conduit 39 and conduit 56 into chamber 52 of accumulator 49 where the increased pressure acts against floating piston 50 to move it upwardly and compress the gas in chamber 51 resulting in only a slight increase in system pressure due to the relatively high compressibility of the gas compared to the liquid. Also, liquid discharges through conduit 58 and throttling valve 53 to restore the system pressure to that obtaining prior to motion of vessel 10. On the other hand, when cylinder 35 moves downwardly in response to downward movement of platform 10, the pressure in chamber 42 will tend to decrease requiring additional liquid at constant pressure to be supplied to chamber 42 to maintain piston 40 at a relatively constant level. This increased volume is supplied by liquid in chamber '52; which is forced through conduits 56 and 39 into chamber 42 by gas pressure contained in chamber 51 and pump 47, now operating at a slightly reduced pressure level, pumps a quantity of liquid per unit of time in addition to that normally pumped when vessel 19 is motionless. Throttling valve 53 also tends to close, diverting this additional flow to chamber 42 as dictated by pilot 60 due to a reduction of pressure in conduits 58 and 59.

Centrifugal pump 47 is operated constantly to force liquid from reservoir 46 into chamber 42 through conduit 39. Once the pressure in chamber 42 has been compensated by the liquid supplied from chamber 52 of accumulator 49, liquid from reservoir 46 is supplied to chamber 52. Also, when excess liquid from chamber 42 feeds into chamber 52, it is later discharged into reservoir 46 through valve 53 by the pilot control 60 sensing the increased liquid pressure in conduit SS'through conduit 59. The excess liquid pressure then is discharged into reservoir 46. In general, small movements of cylinder 35 resulting from slight wave action will be compensated by liquid transmitted from and into accumulator 49;, Whereas large movements of cylinder 35 will be ofliset by pump 47, throttling valve 53, and reservoir 46, as well as accumulator 43.

The pressures in the system must be increased to compensate for the additional Weight of the drill string when lengths of drill pipe are added as the borehole is drilled deeper and deeper or increased or decreased when it is desired to increase or decrease respectively, the Weight it is desired to maintain on the drill bit. Operating pressure ranges for the apparatus for a particular Weight on the bit are a function of piston diameter, suspended drill pipe weight and bit size. Operating pressure may range up to twice the pressure available in commercial gas cylinders, about 4900 psi, depending on the designers desires.

The sensitivity of control of the position of piston 40 depends on the compressibility and volume of gas contained in accumulator 4%, the capacity of pump 47 and the sensitivity of pilot control 60 and throttling valve 53. As mentioned supra, to maintain sensitivity of accumulator 49 as the operating pressure level increases, it is necessary to add gas to chamber 51 as the depth of the drilled hole increases and to supply gas to chamber 51; an air receiver continuously charged by an air compressor may be used instead of the gas bottles 68 shown.

Having fully described the nature, objects, and elements of my invention, I claim:

Apparatus for maintaining substantially constant tension on well equipment such as drill pipe and the like suspended in a well bore from suspension apparatus mounted on a floating offshore structure comprising:

an elongated cylinder and a piston slidably arranged in said cylinder interposed between said suspension ap paratus and said well equipment;

means for providing constant liquid pressure to said cylinder to maintain substantially constant tension on said well equipment including an accumulator comprising a chamber having a movable, pressure responsive member dividing said accumulator into first and second chambers, means for supplying gas under pressure to said accumulator first chamber, said accumulator second chamber containing liquid in fluid communication with said cylinder; means for increasing the gas pressure in said accumulator first chamber as the Well bore is deepened to maintain constant sensitivity of said apparatus; said accumulator first chamber being provided with a gas-relief valve for reducing fluid pressure in said accumulator second chamber;

a liquid reservoir; and a constant speed, variable volume pump for supplying said cylinder with liquid at a constant selected pressure, said reservoir liquid being in fluid communication via said pump with said accumulator second chamber, and means responsive to increased liquid pressure in said cylinder for releasing liquid to said reservoir from said cylinder and also from said accumulator second chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,109,297 McMurry et al Feb. 22, 1938 2,214,816 Harrington Sept. 17, 1940 2,214,817 Harrington Sept. 17, 1940 2,595,248 Greer et al May 6, 1952 2,945,676 Kammerer July 19, 1960 2,945,677 Kammerer s July 19, 1960 

